This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-359080, filed Dec. 17, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a coating film forming apparatus for forming a coating film on a substrate such as a semiconductor wafer, an LCD substrate (a glass substrate for a liquid crystal display), or the like by applying a coating solution thereon.
In the process of fabricating a semiconductor device or an LCD, resist treatment is performed for a substrate by so-called photolithography. In this technology, a series of processes, for example, of coating a semiconductor wafer (hereinafter referred to as a wafer) with a resist solution to form a solution film on its surface, exposing the resist film through the use of a photo mask, and thereafter performing developing treatment to obtain a desired pattern are performed.
The coating process of the resist solution in the aforesaid processes has been hitherto performed by a so-called a spin coating method. This method is the following method: A rotatable spin chuck is provided in a cup surrounding the entire side thereof; a wafer is horizontally suction-held by the spin chuck; and a resist solution is spread by the centrifugal force of the wafer by supplying the resist solution onto the wafer W from a nozzle above the central portion of the wafer while rotating the wafer W to thereby form a solution film on the entire wafer.
However, the line width of a resist pattern formed is proportional to the film thickness of a resist film and exposure wavelength. Therefor, to cope with the formation of a finer pattern which has been demanded increasingly in recent years, it is necessary to make the solution film thinner as much as possible, and a thinner film can be obtained by increasing the rotation speed of the wafer in the spin coating method.
In the aforesaid method, however, the wafer is rotated at a high speed, and hence a peripheral speed at an outer peripheral portion is higher that that at an inner peripheral portion, thereby causing a problem that turbulence of air occurs at the outer peripheral portion specially when the wafer is increased in size. This turbulence causes film thickness to change to thereby make the film thickness on the entire wafer ununiform, thus hindering the formation of the finer pattern.
Further, since the resist solution is spread by being blown away from the central portion of the wafer W toward the peripheral edge thereof in this method, the amount of the resist solution wasted by scattering from the peripheral edge portion toward the cup is large. Furthermore, there arises a problem that the resist solution applied to portions such as the peripheral edge portion other than a circuit formation area and the resist solution adhering to the cup due to scattering are cured to thereby cause particles.
For the aforesaid reasons, a coating unit without using the spin coating method is thought up. For example, a unit shown in FIG. 14 includes a mask 12 covering the entire area except a circuit formation area 11 of a wafer W and supplies a resist solution to the circuit formation area 11 only in a way similar to a picture drawn with a single stroke of a brush by supplying the resist solution to the wafer W from a nozzle 13 provided above the mask 12 with the nozzle 13 being reciprocatingly moved in an X-direction and the wafer W being intermittently moved in a Y-direction.
Since the wafer is not rotated in this unit, the aforesaid disadvantages are eliminated, whereby coating with no waste can be performed. However, the resist solution is discharged to the surface of the mask 12, and with the repetition of treatment, the thickness of the resist film increases and the resist film peels off, which causes particles. Hence, it is required to remove the mask 12 in predetermined timing, replace the mask 12 with a cleaned mask, and clean the contaminated mask 12 in a cleaning unit provided separately. Therefore, there arise problems that a space for cleaning the mask 12 and a space for making cleaned masks wait are necessary, resulting in an increase in the size of the unit, and that work is a troublesome since the mask 12 is cleaned after removed from the coating unit, and mounted in the coating unit after cleaned.
Meanwhile, a unit structured by providing masks 14a and 14b covering only a peripheral edge area corresponding to a scan area of the nozzle 13 at both ends in a moving direction (an X-direction) of the nozzle as shown in FIG. 15 in place of the mask 12 covering the entire peripheral edge portion of the wafer W and changing the distance between the masks 14a and 14b correspondingly to the width of a circuit formation area of the wafer by means of a drive mechanism 16 is thought. According to the structure like this, the nozzle 13 reciprocatingly moves in a fixed movement area, and thus the amount of the resist solution supplied to surfaces of the masks 14a and 14b per wafer is larger compared with the mask 12 shown in FIG. 14, resulting in the more frequent occurrence of particles.
The present invention is made in view of the aforesaid circumstances, and its object is to provide a coating film forming apparatus enabling a high yield of a coating solution, formation of a uniform coating film, moreover easy cleaning of a mask member covering an area other than a coating film formation area, and suppression of an increase in the size of the apparatus.
In view of the aforesaid object, a coating film forming apparatus of the present invention includes: a substrate holding portion for holding the substrate; a coating solution nozzle, provided to face the substrate held by the substrate holding portion, for discharging a coating solution to the substrate; a drive mechanism for moving the coating solution nozzle along a surface of the substrate relatively with respect to the substrate while the coating solution is being discharged to the surface of the substrate from the coating solution nozzle; a mask unit covering a portion other than a coating film formation area of the substrate and including a mask member for catching the coating solution from the coating solution nozzle; and a cleaning mechanism, provided in the mask unit, for cleaning a coating film adhering to the mask member.
According to the coating film forming apparatus of the present invention, the coating solution can be supplied to the surface of the substrate in a way similar to a picture drawn with a single stroke of a brush by the operation of the drive mechanism. Since the mask unit including the mask member for catching the coating solution from the coating solution nozzle and the cleaning mechanism, provided in the mask unit, for cleaning the coating film adhering to the mask member are provided, a cleaning unit for cleaning the mask member does not need to be provided separately, leading to the facilitation of cleaning and a reduction in space.
The drive unit, for example, may be structured to have an X-directional drive section for reciprocatingly moving the coating solution nozzle in an X-direction and a Y-directional drive section for intermittently moving the substrate in a Y-direction relatively with respect to the coating solution nozzle. The mask unit, for example, may be structured to be provided as a pair of mask units which face each other in the X-direction, and each of mask members of the pair of mask units moves in the X-direction correspondingly to the X-directional width of the coating film formation area, and moves in the Y-direction relatively with respect to the substrate correspondingly to the Y-directional relative movement of the coating solution nozzle with respect to the substrate.
The aforesaid structures allow the coating solution nozzle to reciprocatingly move in the X-direction while discharging the coating solution in the form of a line with a small diameter and allow the substrate to move in the Y-direction when the coating solution nozzle is positioned at a turning point, whereby the supply of the coating solution to the surface of the substrate can be performed easily in a way similar to a picture drawn with a single stroke of a brush.
In the present invention, it is preferable to provide a first suction mechanism for sucking a solvent supplied to the mask member and components (dissolved components) of the dissolved coating film, and moreover it is preferable to provide a second suction mechanism for sucking the solvent which spilled to a bottom face of a case body and the dissolved components. Thus, it becomes possible to remove the coating solution adhering to the mask member certainly.
The cleaning mechanism may be structured to include a solvent nozzle, provided separately from the mask unit, for discharging a solvent to the mask member to dissolve the coating film. For example, a structure in which the solvent nozzle is combined so as to move with the coating solution nozzle is also possible. Incidentally, an ultrasonic vibrator for applying an ultrasonic wave may be provided in the solvent nozzle.
Further, the coating film forming apparatus of the present invention can be structured to include a solvent supply section for supplying the solvent to the surface of the mask member so as to form a flow in the form of a film and a third suction mechanism, a suction port of which is formed in the surface of the mask member, for sucking the solvent and components of the dissolved coating film from this suction port.
Furthermore, a portion facing at least a movement area of the coating solution nozzle in the mask member may be structured by an absorber (cleaning mechanism) for absorbing the coating solution. This structure corresponds to the coating film formation area of the substrate and it is suitable for the mask member covering the entire peripheral edge portion of the substrate. In this case, a structure including a fourth suction mechanism for sucking the coating solution absorbed by the absorber is desirable.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.